This invention relates to a process for removing nitrous oxides from a gas, and more particularly, to such a method in which the gas is passed through a fluidized bed reactor operating in a manner to remove the nitrous oxides from the gas.
Combustion systems utilizing fluidized beds as the primary source of heat generation are well known. In these arrangements, air is passed through a bed of particulate material, including a fossil fuel such as coal and an adsorbent for the sulphur generated by the combustion of the coal, to fluidize the bed and promote the combustion of the fuel at relatively low temperatures. An added advantage is that the fluidized bed combustion process has the ability to produce lower emissions of nitrous oxides (NOx) than conventional combustion systems.
In U.S. Pat. No. 4,308,810, assigned to the assignee of the present invention, an apparatus and method is disclosed in which the reduction of NOx emissions from a fluidized combustion system is reduced even further from the reduction achieved by the standard fluidized bed. In this technique, the amount of air added to the bed is less than the required for complete combustion resulting in the production of extremely low NOx. To reduce carbon monoxide and methane to acceptable levels, overfire air is added above the upper surface of the fluidized bed which results in a large reduction of the carbon monoxide with little or no increase in the already low NOx emissions. The bed material includes an adsorbent for the sulfur generated by the combustion of the fuel, and the above technique does not compromise the sulphur capture performance.
However, these prior art techniques have been limited to the reduction of NOx from the self-generated gases in the bed, and have not been applied to the reduction of nitrous oxide from external gases such as the gases received from an oil refinery or the like, which are laden with NOx and with sulphur.